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Inhibition of Pseudomonas aeruginosa by hyperbaric oxygen: interaction with mouse peritoneal exudate cells
Abstract:
High-pressure oxygen (HPO) therapy for Pseudomonas aeruginosa infections of burn wounds has not been as effective as in vitro studies predicted. Mitigation of HPO toxicity for P. aeruginosa by nutrients present at the burn site could explain the lack of in vivo success. Alternatively, HPO-induced depression of host defense mechanisms could negate beneficial effects arising from HPOs known toxicity for P. aeruginosa. Accordingly, mouse peritoneal exudate cells (PEC), preincubated for 24 h in 1 atm of air-CO(2), were used to study the in vitro effects of HPO or air-CO(2) on phagocytosis of P. aeruginosa or sheep erythrocytes (SRBC). Subsequent 2-h exposures of PEC to increasing numbers of bacteria, in an air-CO(2) atmosphere, decreased the percentage of bacteria cleared as well as PEC viability. Similar exposures of PEC to bacteria in an HPO atmosphere prevented the loss of PEC viability and increased bacterial clearance. In control experiments, increasing the number of SRBC relative to PEC decreased the percentage of SRBC cleared without decreasing PEC viability, as determined under air-CO(2); short (2 h) exposure to HPO did not affect SRBC clearance. Microscopic examination of PEC indicated that a 24-h preincubation in HPO decreased the percentage of PEC which could ingest SRBC during subsequent experimental exposures (2 h) to air-CO(2) or HPO. These data suggest that short periods of exposure to HPO promote the ability of PEC to clear pseudomonads by adversely affecting the bacteria. This in turn prevents a pseudomonad-induced depression of PEC viability and function. In contrast, prolonged HPO exposure may be detrimental to phagocytic activity.
Insights
High-pressure oxygen (HPO) therapy shows promise for Pseudomonas aeruginosa infections. Short HPO exposure enhances host immune cell function and bacterial clearance, improving outcomes in burn wound infections.
Area of Science:
- Immunology
- Microbiology
- Hyperbaric Medicine
Background:
- High-pressure oxygen (HPO) therapy's effectiveness against Pseudomonas aeruginosa in burn wounds is limited.
- Nutrient-mediated mitigation of HPO toxicity or HPO-induced host defense depression may explain this discrepancy.
Purpose of the Study:
- To investigate the in vitro effects of HPO on host immune cell (peritoneal exudate cells - PEC) phagocytosis of P. aeruginosa.
- To determine if HPO impacts PEC viability and function in the context of bacterial infection.
Main Methods:
- Mouse PEC were exposed to P. aeruginosa or sheep erythrocytes (SRBC) under varying atmospheric conditions (air-CO(2) vs. HPO).
- Bacterial clearance, PEC viability, and phagocytic activity were assessed after short-term (2-h) and long-term (24-h) HPO exposures.
Main Results:
- Short-term HPO exposure enhanced PEC bacterial clearance and preserved PEC viability against P. aeruginosa.
- Prolonged HPO preincubation impaired PEC's ability to clear SRBC, suggesting a detrimental effect on phagocytosis.
- HPO did not affect SRBC clearance in control experiments, indicating specificity towards bacterial interactions.
Conclusions:
- Short-term HPO exposure enhances host immune cell function against P. aeruginosa, potentially by impairing bacterial defenses.
- This improved clearance prevents pathogen-induced immune cell dysfunction, offering a therapeutic benefit.
- Prolonged HPO exposure may negatively impact phagocytic capacity, necessitating careful treatment duration considerations.